The present invention relates to a new and improved construction of apparatus for simultaneously viewing both transparent positives or images, hereinafter conveniently broadly referred to as diapositives, and front viewed pictures.
One of the most difficult problems in the graphic arts is to appraise the quality of prints which have been produced from transparent copies. This is so owing to the different reproduction processes employed in the case of photographs and prints, especially because of the considerably greater density of the border in the case of a diapositive in relation to a printed picture image.
In order to be able to objectively appraise the comparison of printed copies and prints there have heretofore been proposed illumination standards. Such standards are set forth, for instance, in the publication of American National Standard Institute entitled "Viewing Conditions for the Appraisal of Color Quality and Color Uniformity in the Graphic Arts". However, the preconditions for the general compliance with such standards is that there be available viewing devices which satisfy these requirements and that such devices be as wide disseminated and available as possible.
Heretofore there were only known to the art separate viewing devices for handling transparent images or direct or front viewed images and which satisfied these illumination standards. However, in order to be able to simultaneously view with such devices diapositives and front viewed images or pictures the rear viewing device had to be erected in the illumination field of the front viewing device in such a manner that a portion of the light complying with the illumination standards and emanating from the front viewing device also impinged the rear viewing device. Yet since the separate rear viewing device and front viewing device generally cannot be accommodated to one another -- normally they emanate from different manufacturers-- the reproducability of the mutual spatial arrangement of both separate viewing devices and which is governed by such standards is not ensured for, and thus the ability to judge the quality obtained in this manner is dubious.
A further drawback, especially of the heretofore known front viewing devices, resides in the fact that such are generally designed for relatively large image or picture formats, and therefore, the equipment itself is correspondingly voluminous or bulky, and hence non-transportable i.e. must be left in place where erected. Owing to their considerable space requirements and especially because of their relatively great cost these devices are generally only suitable for use by large firms, not however for small and medium size firms, and certainly not at all by their customers.